Water heater control system and thermal retarder therefor



1945- c. M. OSTERHELD 2,375,379

WATER HEATER CONTROL SYSTEM AND THERMAL RETARDER THEREFOR Filed Now 2 2, 1945' 3 Sheets-Sheet l fly i giARk/l 222L212 M ATTORNEY y 1945- c. M. OSTERHELD 2,375,379

WATER HEATER CONTROL SYSTEM AND THERMAL RETARDER THEREFOR Filed Nov. 22, 1945 3 Sheets-Sheet 3 mum ((((((((((llllllllllll))))))) ATTORNEY INVENTOR. f'/@ 99 CLAR/f Gama/7 :40

Patented May s, 1945 ws'raa mares-common SYSTEM AND THERMAL aa'rsanaa 'rnsasron Clark M. Ostefrheld, Stoughton, Wis, minor to McGraw Electric .20 Claims. My invention relates to electric heating-and mn r,

. poration of Delaware 7 Application November 22. 1948,

, 111., a cor- Sei'lfl No. 511,886

1 ('01. sis-4s) particularly to the control of hot water heating a systems.

An object of my invention is to provide a'control system for a hot water tank that shall include a thermal retarder' heater control switch unit for delaying energization of the heater for a preset time under certain operating conditicns.

Another object of my invention is to provide a control system for a hot water tank that'shall be eflective to cause-immediate energization of the heater at the start of an oil-peak period in case a relatively large quantity of hot water has been withdrawn from the tank and that shall delay energization of the heater for a predetermined time period of delayin case a relatively small quantity only has been withdrawn from the tank.

Another object of my invention is to provide a thermal retarder heater control switch unit comprising a pair ,of dissimilarly thermally-responsi've elements one of which is adapted to be subjected to the temperature of the water in the tank and the other of which is adapted to be heated by a heating coil and a heater control switch mechanically pivotally supported and aetuable by saidpair of elements.

Another object of my invention is to provide a thermal retarder heater controtswitch unit comprising a pair oi? dissimilarly thermally-responsive elements, 'one of which is mounted on a support adapted to be secured on a tank intermetriccircuit showing manual control of' the retarding period,

' 4 is .a iragmentary sectional view on an enlarged scale showing my improved thermal retarder in side view Fig. 5 is a view in front elevation of the parts shown in Fig. 4, the section extending through the casing,-

Flg. 6 is a top plan view of the parts shown in Fig. 4 with the section extending through the casing, Fig. 7 is a section therethrouch on the line 1-1 of Fig. 9,

Fig. 8 is a fragmentary front view of part of Fig. 10 showing the control button: I

Fig. 9 is a vertical, sectional view taken on the line l-J of Fig. 5, and,

Fig. 10 is a fragmentary view in side elevation of the parts shown in Fig. 9 under certain operating conditions. i

I have illustrated in Figs. 1 and 2 a domestichot water tank together with a diagram of connections of my improved control system and have elected to show a domestic hot water tank H which is provided with a lower cold water inlet and an upper hot water outlet-ll. The tank may surrounded by any suitable heatinsulating material ll, such as mineral wool, and an outside casing ll may be provided. Supports 2| may be provided all in a manner now well known in the art.

diate the ends thereof and the other of which is mounted on a heat-insulating support and a heater control switch adapted-to be actuated by said elements to closed position when thefirst element is subject to cold water and the second element is at substantially room temperature and to be actuated to open position when the first element is subject to'hot water and the second element is at substantially room temperature.

Other objects of my invention will either be apparent from a description of one form now preferred by me or will be pointed out in the course of such description and set forth particularly in the appended claims.

In the drawings, I

Figure l is a sectional view of a hot water tank showing parts of my control system applied thereto,

Fig. 2 is a diagram of the electric circuits of I 'my improved control system,

Fig. 3 is a fragmentary diagram of the elec- I provide preferably but not necessarily, a

single electric heater II which may be of any suitable or desired type and is shown as being positioned in a tunnel member 25 all in a manner now well known in the art.

I provide a thermally-actuable heater control switch designated generally by. the numeral 21' which is shown to comprise a tubular member 28 with a closed inner end having its outer end.

suitably secured in an opening in thetank ll adjacent the lower end portion thereof in a water-tight manner. I provide an expansion rod 3| therein which is adapted to engage and move a resilient contact arm 33 having a contact member thereon adapted to engage with and be disenga ed from a cooperating contact member on a relatively rigid contact arm 35.

The two contact arms 33 and" are supported on the outside of the tank as by means of blocks 31 of electric-insulating material. The rod 3| is shown, in Fig. 1, as of relatively short length such as it will have when subject to cold water whereby the contact members or arms II and .35, will be in electric-conducting engagement with each other, I do not desire to be limited to the particular details shown, since these are illustrative only, but may use any other form of thermally actuable switch effective for the same purpose.

I provide also a thermal retarder heater control switch unit designated by numeral 39 which will be hereinafter described in detail.

I provide a continuously operative timer fill comprising a subsynchronous motor having a worm 45 on its rotor shaft, which worm is adapted to engage aworm gear 41 which is mounted on a shaft 49 whichshaft is provided with suitable bearings not shown in Fig. 2.

I provide a cam disc ill on shaft 19 having the greater part of its peripheral surface of a fixed.

outside radius but having a portion'thereof of a somewhat greater radius, which portion is designated by 53. The peripheral extent of portion 53 is substantially that of the usual aftermidnight oiT-peak period, it being understood that the design of timer 4! is such that the cam disc 51 rotates through 360 during a twentyfour hour day.

I provide a heater circuit switch actuable by the cam disc which switch includes a substantially rigid contact arm 55 and a resilient contact arm 51 which latter arm has a lug 59 ofelectric insulating material secured thereto to be engaged by the cam disc. 5| The two contact arms 55 andi'l may be held in proper operative positions relatively to each other by a block SI of electricinsulating material. It is to be understood that the showing of timer 4| is general only and that I may use any timer-controlled switch effective for the same purpose.

An electric supply circuit includes conductors 63 and 65 and it will be noted that contact arm 55 is connected to conductor 63 while contact arm 51 is connected by a conductor 61 with a contact terminal 69 of the thermal retarder unit 39. k A second terminal ll of the ther: mal retarder unit is connected to one terminal of heater 23 by a conductor 13. l The contact arm 35 is connected to the other terminal of resistor heater 23 while contact arm 33 is connected by conductor with the "supply circuit conductor 65.

It will be obvious that the entire control system is deenergized during the on-peak period which for illustrative purposes may be considered to extend from say 6 a. m.- to on orabout 12 midnight,

the off-peak period being therefore on the order of six hours.

Referring now to Figs. 4 and 10 inclusive I have there illustrated one form of-a thermal retarder heater control switch unit 39 constituting a means fordelaying energization of the heater 23 under certain operating conditions. The thermal retarder 39 includes a bracket I! which is of a metal or alloy having high heat conductivity and which may be secured in heat-conducting engagement with the outer surface of the tank at substantially the mid-portion thereof as'by screws 18 having screw-threaded engagement with a block I9 of high heatsconducting metal or alloy secured to the tank i I by welding seams 80 (see Fig. 9). On bracket 11 I provide a vertically-extendingfirst expansion rod 8| of high expansion metal, such as aluminum, which in order that it may be in good heat-receiving relation relatively to the bracket 11, may have a reduced lower end portion 83 fitting tightly into a bore 85 in bracket 11. The upper end portion camera of rod iii is provided with a reduced end portion 8i and a short laterally-extending lug or arm 88 is rigidly mounted thereon.

I provide a block M of heat-insulatin material, which block may be of substantially rectangular shape in cross section which is secured againstbraclret W as by screws 93. I provide a second vertically-extending expansion rod 95 of lower thermal expansion, such as a nickel steel alloy, which has a central bore ill" therein and which has its lower end portion 99 extending into'a circular aperture in block Hi. The upper end portion of rod 95 is provided with a portion Wu of reduced diameter having a short arm or lug i0! thereon held rigidly by any suitable or desired means. A heat-insulating cover or outer casing N12 is provided around second rod 95. The two expansion rods extend parallel to each other.

While the expansion rod iii is preferably made of aluminum and the second expansion rod 95 is preferably, made of a nickel-iron alloy, so that 1 its linear thermal expansion is less than that of rod 8| and may be one-half that of rod 81; I may use any other materials in place thereof, having the same relative linear-expansions.

I provide a low-wattage heating coil 103 within the bore 91, the end portions or leads of heater I03 being secured to terminals H15 on a blocir I01 of electric-insulating material secured to bracket H. One terminal of coil W3 is connected to contact arm 36 by a conductor I08, while the other terminal of coil I03 is comiected to conductor El and terminal 69 so that coil W3 is energized as soon as and when arms 51 and 55 of the timer switch .and arms 35 and 33 are engaged with heat from coil Hi3, I do not desire to be limited thereto since I may use the coil M3 to effect heating of the second expansion rod 95 by electromagnetic effects such as hysteresis. This, of

- course, is dependent upon the use of alternating current to traverse the coil I03. While I may let the coil I03 remain in the bore ill, its electro- A magnetic heating effect will be relatively very small, and if found to be too small to effect the desired heating of the second rod 95 in the desired time I may locate the coil I03 around the outside of the rod 95. Where the words heating coil" are used in the specification and in the claims it is to be understood that heating of I of being of unequal length, the member Hi9 being made of two spaced parallel arm portions each of substantially L-shape. The shorter arm portion is pivotally supported by suitable pins HI and H3 in lugs 89 and IIJI. A second toggle arm 5 is pivotally connected with arms I09 at their lower end and an over center spring I I1 extends to either side of the junction of arms I i5 and arms I09, being secured to the'arm H5 and toacrossbarll9inarmslil9.- 1

Referring to Fig. 4 of the drawings I have there shownthe position or a contact bridging member ill which is insulatedly mountedon a.

-water and the heating coil for rod 35 has been block I23 secured to the lower end of .arm III, as being in engagement with contact members II and 83. The conditions as to temperature of the two expansion rods II and 35 is that either the temperature of the two rods is substantially that or the ordinary room, say on the order of 70 F., under which conditions the length of the two rods is substantially the same with the result that contact bridging member I2I is in engagement with contacts 69 and II andthe switch is therefore incircuit-closing position. Further, Fig. 4 illustrates the position occupied by the contact bridging member I2I when the temperatures of expansion rodsBl and 85 are relatively high, that is when rod 3| is subject to the temperature of hot water in the tank II, which for illustrative purposes may be taken as 150 F. to 170 F., while the temperature of rod 35 is such that its length is substantially equal to that of rod 3| having been heated by the energized-coil I03 to a temperature on the order of 300 F.

Referring now to Fig. 9 of the drawings I have there illustrated the position of the snap acting I switch and particularly of the contact bridging member I2I when rod 8| is subject to the temperature of hot water in the tank but coil I03 is either deenergized or has been energized for only a relatively short period of time. Block I23 is in engagement with a stop member comprising a bracket I25. held rigidly against block 9| and provided with an adjustable stop screw I21 having a lock nut I23 thereon. Under theseconditions the switch is in deenergizing position. f

My thermal retarder switchunit comprises a snap acting switch actuated by a pair of dissimi- .larly thermally-expanslble elements, so that it may operate in the desired manner under oper-,

Thus the switch must be in ating conditions. closed position when the tank is filled with cold energized only a shorttime. 1!.so much hot,

"water has been withdrawn from the tank that the thermal retarder is subject to'water having a temperature on the order of. 115 and the heating coil torrod 3| has been energized only a short length of time, the switch must also'be in closed position. I! on the other hand the tank is full of hot water having a temperature or. say

150 F. and has been standing under such condition tor a length of time sumcient to cause the temperature or both rods II and "to reach a value of 150 I". or slightly less, the switch must remain in open position.

just been tilled with cold water. If it be assumed that such filling was done during the onpeak period, contact arms I! and 51 would be out or electrical engagement or connection with each other, but just as soon as cam disc portion 33 engaged lug 53 on arm 51 closure of the circuit would ,be effected since rod 8I would be relatively short (being at'the temperature of the cold wa ter), .rod 90 would also be relatively short since it would also be at substantially room temperature androd 3| would also be at thetemperature of the coldiwater with the result that contact arms 33 and would be in electrical engagement. The result of this would bethat energization of heater 23 would be effected immediately upon closure'oi the timer controlled switch.

Heating of the .water in the tank would there- 'fore progress and it would be expected that substantially all of the water in the tank would be heated before or by the end of the oil-peak period. When substantially all of the water in the tank is hot, the first thermally-actuable heater control switch 21 will open to interrupt th heater circuit.

temperature rise of expansion rod 95 wouldbe such that its length would be substantially that 4 of expansion rod 8| whichis subject to the temthe second expansian rod 05 has been heated to To cause the thermal retarder switch to move from the 'open to the closed position as when it is subject to hot water in the tank at a temperature oi 150 F. or slightly more, the second expansion rod must be heated to a'temperature of 300 F.

or more, depending on its thermal expansivit as comparedtothat oi the flrstrodll.

The thermal retarder is provided with a casing III and as has already been hereinbetorm stated is secured against the outer suri'ace of the hot-water tank II at substantiallythe mid-' portion thereof in'an ob in theouter cas-' in; II and-the heat-insulating material n which opening may be closed by a.closure I33. I may provide a substantially similar closure ill for the lower thermal heater control switch 21.

I may provide further a block I31 of electricinsulating material which marreet upon a portion of the outer case II and have'terminal members I3! mounted thereon in order to permit oi outside electric-circuits thereto.

Let itncw'be assumed-thumbs tank II has perature of the water in the tank. If the thermal retarder 33 is supported on the tank atsubstantlally the mid-portion thereof, the thermal retarder wouidbe subject to the temperature of hot water at about the end of about three hours and rod 35 would not be fully expanded when rod 8| is fully'expanded and the switch would be moved to the open circuit position shown in Fig. 9. This would deenergize the heater 23 temporarily until its maximum temperature, which would occur one hour later. This would cause reclosing of the .thermalretarder switch an the heater 23, which reenerg ation would continue until opening of the timer controlled switch at the end or the-o'fl-peak period.

1 Let it be assumed that at 12 midnight, the start 7 of the oil-meal: period-and the closure of the.

timer controlled switch, only a relatively small amount of hot water has. been withdrawn from the tank just suflicient to subject the lower thermalswitch 21 to cold water. In this case contact arm 33 will have-been moved into engagement with contact arm 3!, expansion rod II- will still be subject to hot water and rod 00 will be'relatively short, that is at the start or the oil'- peak period. In this case energization of the small heater in m rod u will continue for a period of say substantially four hours until rod 0| expands suniciently tocause closure of the thermal retarder switch and energization of the heater 23 for a short length'oi time, on the order of two hours, which is sumcient'to heat the water in the lower end portion of the tank before the position.

Let itbe assumed. on the other hand, that sufflcicnt hot water was withdrawn 1 the tank so that the thermal retarder was timer controlled switch is again moved to open reenergization of J tooold' water with the'result that the thermal retarder switch was also in closed position as well as the lower thermal heater controlled switch 21. The result would be that the heater 23 would be energized substantially immediately upon closure of the timer controlled switch at the start of an ofl-peak period. If it would require say only two hours to heat up enough water to subject the thermal retarder to hot water, the thermal retarder switch might be temporarily moved to open position but with the continued energization of the heater lllt expansion of rod Ht would continue until the thermal retarder switch would again be moved to circuit-closing and therefore heater-energizing position, with the result that heating of the water in the lower portion of the tank, that is below the thermal retarder, would continue until substantially all of the water in the tank would be heated to a predetermined temperature, say 150 beforethe end of an offpealr period.

It is obvious that changes may be made in the adjustment of the rheostat J ll to vary the timer required to raise the temperature of the second expansion rod to its maximum value and that the wattage of the tank heater has an eilect on the length of time required to heat the water in the tank, the greater the wattage of the heater the shorter the time necessary to heat all of the water to a temperature or d F.

It is therefore obvious that my improved control system and particularly the thermal retarder heater control switch unit provides a relatively simple and highly efficient means for permitting immediate energlzation of the tank heater in case a relatively large amount of hot water was withdrawn from the tank during the day and delaytrolled by a timer controlled switch and by a heater control switch.

It is further obvious that while the timer is shown as being provided with means for fixing a single oft-peak period only, two or more oil-peak periods may be fired thereby.

Various modifications may be made in the system embodying my invention without departing from the spirit and scope thereof and all such modifications coming clearly within the scope of the appended claims shall be considered as being covered thereby.

I claim as my invention:

1. Awater heater control system for a domestic hot water tank subject to'withdrawals of hot water during a twenty-four hour day comprising an electric heater adapted to be energized by an electric circuit having reduced demands for energy after midnight, a thermally-responsive heater control switch subject to tank water temperature at the lower end portion of the tank, a thermal retarder heater control switch unit camera second rod, a heater control switch actuable by said two rods, a continuously operative timer and a heater circuit switch adapted to be closed by said timer during said period of reduced demand,

said two heater control switches and said circuit switch being jointly efiectlve to cause energizetion of said electric heater simultaneously with the closing of the circuit switch in case the thermall retarder is subject to cold water and said thermally-responsive heater control switch being effective to cause deenergization of said electric heating means when the tank is full of hot water.

til

2. An old-peak water heating system for a hot water tank having an electric heater, comprising a continuously operative timer, a first heater control switchadapted to be moved into and held in closed position by said timer during an 0th peels period, a second heater control switch in series circuit with said timer-controlled switch subject to tank water temperature adjacent to the lower portion or" the tank and adapted to be movedinto closed position when subject to cold water, a third heater control switch in series cincuit with said first and second switches and means to cause closing or" said third switch with a predetermined time delay period after the start of an obi-peel; period in case said second switch only-is subject to cold water, said means comprising a, first thermally-eirpansible means adapted to be mounted on a tank intermediate the ends thereof, a second thermally-expansible means heat insulated from the tank, a heating coil for said second thermally-expansible means controlled by said timer controlled switch and said second switch to be energized at the start of an off-peak period to cause thermal expansion of said second thermally-expansible means and closing oi said third switch'alter a predetei mined time clelay period with attendant energizetion of said electric heater.

3. A water heater control system for a domestic hot water tank subject to withdrawals of hot water during a twenty-tour hour day comprising an electric heater adapted to be energized by an electric circuit having reduced demands for energy after midnight, a thermally-responsive heater control switch subject to tank water tem perature at the lower endportion oi the tank, a thermal retarder heater control switch unit mounted in heat-conducting relation to the tank intermediate its ends and including a first expansion rod subject to tank water temperature, a second expansion rod, a heating coil for said second rod, a heater control switch actnable by said two rods, a continuously operative timer and a heater circuit switch adapted to be closed by said timer during said period of reduced dethe closing oi the circuit switch in case the ther mal retarder is subject to cold water.

4. A water heater control system for a domestic hot water tank subject to withdrawals of hot water during a twenty-Iom' hour day comprising an electric heater adapted to be energized by an electric circuit having reduced demands for energy after midnight, a thermally-responsive heater control switch subject totank water temmounted in heat-conducting relation to the tank intermediate its ends and including a first ex-' perature at the lower end portion of the tank,

a thermal retarder switch unit mounted in heat conducting relation to the tank intermediate its ends and including a. first expansion rod subject to tank water temperature, a seconderpansion rod, a. heating coll for said second rod, a heater 7 water.

tinuously operative timer and a heater circuit switch adapted'to be closed by said timer during said period of reduced demand, said two heater being jointly effective to cause energizatlon of said electric heater with a predetermined p'eriod of time delay after closing of said circuit switch in case the thermal retarder is subject to hot 5. A system as set forth in claim 4 and including means for varying said predetermined period 0! time delay. 1

6. .A water heater control system for a domestic prising an off-peak timer-controlled heater-control switch, a. thermally-responsive heater control switch adapted tobe subjected to tank water temperature at the lower portion of the tank and ;a thermal-retarder heater control switch comprisinga pair of dissimilarly thermally-respon- 'sive elements, one of which is adapted to be subjected {to tank water temperature intermediate the ends of the tank. v "7. A water heater control system for a domestic hot water. tank having an electric heater, comprising an cit-peak timer-controlled heater-'control switch, a thermally-responsive heater control i switch adapted to be subjected to tank water temperature at the lower portion of the tank and a thermal-retarder heater control switch adapted to be subjected to tank water temperature intermediate the ends of the tank, saidthree switches.

being connected in series circuit with each other 5 to jointly control said heater, and 'said thermal retarder switch being eflective to-cause energ'ization of said heater immediatelyafter closure of Y theoil-peak switch in case of predeterminedconditions as to the amount of hot water in the tank. 8. A water heater control system for a domestic hot water tank having an electric heater, comprising an off-peak timer-controlled heater-con- I trol switch,'a thermally-responsive heater control switch adapted to be subjected to ,tankwater temperature at the lower portion of the tank and a thermal-retarder heater control switch adapted to be subjected to tank water temperature intermediate the ends of the tank, said three switches being connected in series circuit with each other to jointly control the heater, and said thermal retarder switch being elective to cause energization. oi! said heater immediately after closure of the oil-peak switch in case oi 'predetermined conditions as tothe'amount of hot water in the tank and being effective to cause ener-' gization of said heater with a predetermined time 7 delay period under other'predetermined condia. thermally-Wye heatercontrol n w in commune tions as to the amount of hot water. in the j 9. A water heater control system for a domestic hot water tank having an. electric heater. som prising an oil-peak timer-controlled heater-con m1 switch, a thermally-responsive heater control switch adapted to be subiectedto-ta'nk water umperature at the lower portion-o! the tank and athermal-retarder heater control switch adapted .tO be subjected to tank water temperature intermediate the ends or the tank, said three switches being electrically connected inseries circuit with each other and with the electric heater and said thermally-responsive switch being elective todeenergize said heater when substantially all of thewaterinthetankilhot.

mAwaterheater-controlsystemiorahot':

watertank having an-electric heater, comm control switch actimbleby said two rods, a con- ,J v adaptedtobesubj tedtotankwatertemperatureat thelower portion of the tank and a thermal retarder heater control switch unit including a flrst-thermo-sensitive element adapted to'be control switches and said heater circuit switch 6 exchange independent of the tank water and. aux-. iliary means for exchange 0? heatwith said sec- 20 ond element.

12. Jhwater heater control system for a hot water tank-having an electric heater, comprising a thermally-responsive heater control switch subject to tank watq temperature at the lower end portion of the tank and a thermal retarder heater control switchincluding a first thermo-sensitive: element subject to heat exchange with the tankwater intermediate the ends oi the I a second thermo-sensitive elementlsubject to heat exchange independent of the tank water and an auxiliary heating coil for said second element.

13. A water heater control. system for a hot water tank having anelectric heater, comprising a heater circuit adapted to be connected to an elec tric supply line, a thermally-responsive heater control switch for the circuit adapted to be sub- 'jected .totank water temperature at the lower portion of the tank, a thermal retarder heater control switch unit forthe circuit inciuding a first thermo-sensitiye element adapted to be subject to heat exchange with tank water intermediate the ends of the tank, a second'thermo-sensitive element subject tolheat exchange applied independently of tank waterand means controlled by powerlrom the circuit for exchanging heat with said second element. 1

=14. A water heater control system iorahot water tank having an electric heater, comprising a heater circuit adapte'dto be connected to an electric supply line, a thermally-resp nsive heater control switch for the circuit adapted to be subjected to tank water temperature at the lower portion or the'tank.-;; a thermal retarder heater control switch for the circuit including a thermoexchange with the tank water intermedilte the sensitive elementadapted' to be subjected to heat ends of the tankandheat control means'operated by power from the'circuit'ior modifying the effoot of the theme-sensitive element to 'vary the operation of the retarder ihnwaterboatcrcontrolsystem tdrahot water tank having an electric heater, comprismg a-thermaliy-responsive heater control to be 'subjected'toitank water temperaat the lower end portionoi-the tank and a .thermal retarderheatercohtrol switch unit in- 'cluding a first tire element adaptui to be subjected to eetexchansewith tank water intermedicteflthe'ends of the tank andasecond thermo sensitive element hating sheeting means controlled brthe' thermally-remomivc-beater tour the the reoontrolswi I 116. A-water-heater control syihm'ior shot a heater circuit for connection to an electric supply line and two dependent switch units for onening and closing the heater circuit, the first switch unit including a thermo-sensitive element adapted to be subject to tank water temperature at the lower end of the tank and a second switch unit including a first theme-sensitive element adapted to he subject to tank water temperature intermediate the ends oi the tank and a second thermo-sensitive element cooperating with the first element to vary the opening and closing oi the second switch unit and operated hr power ironi v the circuit when the first switch unit is closed.

17. A water heater control system for a hot water tanls having an electric heater, comprising a heater circuit for connection to an electric supply line, a timer-controlled switch for said circuit adapted to he closed during od-peel: hours, a thermally-responsive control switch for said circuit adapted to he subject-to tanlr water to erature at the lower end of the tools, a thermal retarder control switch 'ior said circuit adapted to be mounted in heatconducting relation to the tent: above said thermally-responsive switch and including two dissimilarly thermallr-resnonsive elernenta'the first oi which is subject to heat exchange with tank water and the second of which is subject to heat exchange means independent of the tank water and operated Toy power iroin the circuit when said timer-controlled switch and said thermally-responsive switch are hoth closed.

it. A water heater control system for a hot water tank having an electric heater, comprising a heater circuit for connection to an electric supply line, a timer-controlled switch for aid circuit adapted to he closed during ofteal: hours, a

thermally-responsive control switch for said circult-adapted to he suhlect to tank water ternerature at the lower end at the tends, a thermal retarder control switch for said circuit adapted to be mounted in heat-conducting relation to the tank above said thermally-responsive switch and including two dissimilarly thermally-responsive elements, the first or which is suhject to heat exchange with tank water and the second oi which is subject to' heat exchange means independent ofthe tank water and operated by power from the circuit when said timer-controlled switch and said thermally-responsive switch are both closed andeflective to cause energiaation of said heater immediately after closure of said timer-controlled switch in case said first thermally-responsive element is suhj set to cold water.

19. A water heater control system for a hot ill) corners water tanlr having anelectrlc heater, comprising a heater circuit for connection to an electric sucoly line, a timer-controlled switch for said circuit adapted to he closed during oiilneah hours, a

thermally-responsive control switch ior said cir-,

cuit adapted to he subject to tank water temperature at the lower end oi the tank, a thermal retarder control switch 101' said circuit adapted to he mounted in heat-conductinu relation to the tanlt above said thermally-responsive switch and including two dicwirnilarly thermally-responsive elements, the first oi which subject to heat 'exchange with tank water and the second oi v sive control switch is subject to cold water.

20. A water heater control system for hot water tank having an electric heater, comprising a heater circuit for connection to an electric supply line, a timer-controlled switch tor said circuit adapted to he closed during oil-peel: hours, a thermally-responsive control switch for said circuit adapted to be subject to tank water temperature at the lower end oi'the tank, a thermal retarder control switch for said circuit adapted to be mounted in heat-conducting relation to the tank above said thermally-responsive switch and including two dissimilarly thermally-responsive elements, the first oi which is subject to heat exchange with tank water and the second oil which is subject to heat exchange means independent of the tonic water and operated by power iron; the circuit when said timer controlled switch and said thermally-responsive switch are both closed and edective to cause enersization of said heater immediately after closure of said timer-controlled switch in case said first thermally-responsive element is subject to cold water and efiective to cause energization of said heater with an adjustahly predetermined time delay period in case only said thermally-responsive control switch is subject to cold water, said thermally-responsive control switch being eilective to cause deenergization of said heater when substantially all of the water in the tank is hot.

CLARK M. osrmnrun 

